The present invention relates to a method and apparatus for temperature control. More particularly, the present invention relates to a method and apparatus for temperature control in an exposure apparatus having a plurality of chambers and utilizing a common refrigerant.
In recent years, the trend toward higher integration of semiconductor integrated circuits has highlighted a projection-exposure apparatus having a high resolution reduction projection lens, wherein a pattern formed on a reticle is projected and transferred onto a wafer. Also, this major trend was enhanced by a stepper which moves a wafer by a step-and-repeat method to project and transfer a pattern onto a plurality of exposed areas on the wafer one after another.
Such a high resolution projection-exposure system, however, generally requires the project lens resolution level of the image alignment precision of one-fifth to one-tenth of the minimum line width of the projection lens. Therefore, a slight temperature change due to changes in exposure conditions can directly deteriorate the alignment precision. For example, a lens which resolves a 0.8 .mu.m width pattern for manufacturing an ultralarge scale integrated circuit (ULSI) requires an alignment precision of 0.8-0.16 .mu.m. Therefore, changes in temperatures in air in an optical path of a projected beam can change the refractive index of the projection lens, thereby deteriorating the alignment precision.
For this reason, in a conventional projection-exposure apparatus, a mechanism which controls temperature in each section or enclosure of the apparatus is provided to perform a highly precise alignment. One of the mechanisms uses air as a medium; another mechanism uses liquid as a medium. In a conventional projection-exposure apparatus, the air is used for controlling temperatures in the entire apparatus or in a local section, such as an interferometer. The liquid medium is used for controlling temperature of a projection lens. Note that air as a medium is cooled by a common refrigerant supplied from a freezer. Its temperature is independently controlled by a heater. Also, the temperature of liquid as a medium may be controlled by an electronic cooler.
In the conventional projection-exposure apparatus having such a configuration, a temperature-control system must be constructed for each of the media. This, unavoidably, results in an undesirably large apparatus.